This invention relates to fluid pressure indicators or senders, and more particularly to an improved transducer-type of sender which employs a rheostat for providing an electrical indication of changes in fluid pressures. Even more particularly, this invention relates to an indicator of the type which employs a rolling diaphragm for transmitting changes in the oil pressure of an automotive vehicle or the like to an associated rheostat.
There are several known devices for converting changes in fluid pressure to an electric signal which is representative of the fluid pressure at any given instant. Typically such a device may be used in an automobile to sense oil pressure changes and to send a corresponding electrical signal to a gage or warning device on the dashboard of the vehicle. Many such prior devices used a flat diaphragm to transmit fluid pressure to a reciprocable plunger, or the like, which operated a variable resistance or rheostat in an associated indicator circuit. The problem encountered with the use of a flat diaphragm is that only a very slight motion can be imparted to the associated plunger, so that it has been necessary to employ an additional leverage or cam mechanism to multiply the slight motion of the diaphragm. These multiplying devices, however, require the use of a much larger housing to enclose all of the moving parts.
To obviate this disadvantage a so-called rolling diaphragm has been employed in certain such senders, as suggested for example by U.S. Pat. Nos. 3,069,645, 3,098,209 and 3,504,324. While these pressure senders or transducers employ either annular or planar type resistors in smaller housings, they have the disadvantage that the resistors are of the wire-wound varieties which have their terminations held in place on an associated insulating board by means of rivets, eyelets, or the like. The very small size of the resistance wire that is employed makes it extremely difficult to handle the wire during the winding and terminating operations. Also, in most cases there is no satisfactory means, operable from the exterior of the sender, to calibrate its spring tension.
Moreover, it has also been customary, as in the case of the above-noted U.S. patents, to employ a single electrical contact or wiper, which is shifted relative to the associated resistance coil or rheostat in response to pressure changes in the fluid which is used to operate the device. A single wiper or contact of this type, however, has required extremely high contact pressure to insure that the wiper will be maintained in contact with the associated resistor or rheostat at all times during the operation of the device. This high contact pressure causes rapid wear and short life expectancy for the device.
Still another disadvantage is that rolling diaphragms of the type disclosed in the above-noted patents cannot withstand the torque which is applied to the diaphragm by the associated compression spring during use. Such springs, as they are compressed, have a tendency to unwind and to impart a twisting motion or torque to the associated rolling diaphragm, thereby considerably shortening the life of the diaphragm. In many instances where diaphragms are made from rubber, they frequently tear and develop holes adjacent their marginal edges, thus resulting in an undesirable leakage of fluid through the diaphragm.
It is an object of this invention, therefore, to provide an improved pressure sender or transducer of the type described which is substantially more compact, inexpensive to manufacture, and longer-lasting than prior such devices.
A more specific object of this invention is to provide an improved pressure sender or transducer which utilizes a "printed" resistor of either the plane or cylindircal variety, thereby eliminating the need to employ conventional wound wire resistors or rheostats of the type heretofore employed in such devices.
Still another object of this invention is to provide an improved pressure sender of the type described which utilizes a rolling diaphragm that is connected to an associated indicator circuit by means which substantially eliminates any undesirable twisting of the diaphragm during use.
It is an object of this invention also to provide for an adjustable resistor and improved sliding contact or wiper, which comprises a plurality of inner-connected legs or blades that are slidably engaged with the associated resistor, and which therefore require substantially less contact pressure per blade than prior such wipers.
Other objects of the invention will be apparent hereinafter from the specification and from the recital of the appended claims, particularly when read in conjunction with the accompanying drawings.